I people watch a lot! It gives me a chance to see all the cosplayers that are there and sometimes I can spot a character I was looking for if I stay in one spot for long enough
Wandering aimlessly also is fun, but can get a bit tiring.

I sit at high-traffic areas, walk around. Ask for pictures, strike (Read: attempt to) conversation with people who are by themselves.

It's really my bread & butter of cons, unless it's gaming-centered, there's little that gathers my interest in the organized activities and panels. I normally end up going to those because other people are.

I have a tendency to grab friends and do an impromptu photoshoot when there is a lull in programming. (Fake Protip: putting on a British accent and imitating Nigel Barker makes people respect you more as a photographer!)

I pretty much just hang out with friends, or meet new people. I very rarely go to panels, but I also very rarely get bored. Though I suppose it does help being of legal drinking age, since when things die down a little we go into the bar and have a couple, ehehh.

My group of friends and I tend to either people-watch or play games. If the con we're at has a room devoted to non-video gaming, we tend to head there - it's less hectic/loud than the video game room, and oftentimes there's a couple other people hanging around in there, so you can play a game or two and socialize.

Depending on the size of the con, it changes. Smaller cons I may just try to check out random panels, eat, talk with friends or go to the gaming room. Bigger cons I just wander around looking for cool cosplayers ^.^

hmm, my bf and I get drinks, have a smoke, talk about what happened so far, check out the schedule for what's coming up, and sometimes just sit and read comics we just bought, or admire new toys.
I find myself constantly going over the schedule when I have a free moment, because I need to decide what to do next.

Funny you say photo scavenger hunt and stuff. One of my fave cons actually does various scavenger hunts. There's a photo one, but they also do a Stargate one, and a horror pop culture one. You pick up the list of stuff from a desk near the front of the hotel, and over the weekend, they gradually add the things on the list to con area. the SG hunt is for the constellations and sigils from the show, which are printed on little squares of laminated paper. They stick them all over the hotel, like under stairs, on pay phones, and other random places, and you run around looking for them and writing down the code on your piece of paper. First one to be most complete wins a little prize on Sunday. It sort of encourages you to stay all weekend.

I usually just wander the halls, and wander into panels sometimes...usually I come across a panel I really like. For example, the Durarara!! panel where all the English voice actors came to. That was really awesome.

In the down time at my cons i usually make sure i eat something and have some water (Im one of those people who sort of forgets to eat and drink and i've had moments where i've almost blacked out..)
I take a stroll down all the stalls and mostly just look at things.
My friends and I chill out and play card games or just chat.
I've caught myself just watching people in down time before, i like to see how others are acting etc.
Uhhhh panels sometimes..

Sometimes I just leave. Especially if my back or feet hurt lol.

I like the idea of a Scavenger Hunt though. I might have to try that next con.